a) Field of the Invention
This invention relates to a discharge assembly and method for generating a dischargeable effluent from spent photographic liquids; more especially the invention is concerned with such a discharge assembly and method for generating a dischargeable effluent from separate feeds of a colour photography, de-silvered spent photographic fixer liquid containing iron ions, and a colour photography, spent alkaline photographic developer liquid.
b) Description of Prior Art
Colour photography processing employs a developer liquid which develops the image in an exposed film, and a fixer liquid which fixes the developed image.
The developer liquid is highly alkaline typically having a pH of 10 to 11; and the fixer liquid is substantially neutral, typically having a pH of 6.5 to 7.5. The two liquids are recycled in use until they are considered spent.
Silver ions from the photographic film accumulate in the spent fixer, and are recovered by exchange with iron whereby silver metal precipitates from the spent fixer liquid, to form a spent fixer liquid loaded with iron ions. The spent fixer liquid also has a natural content of iron ions derived from an iron ion content in the original fixer liquid.
Photographic processing sites typically may only have access to a single drain for discharge of the spent fixer and developer liquids, and thus it would be convenient to discharge them together into the drain.
When the spent fixer and developer liquids contact each other, especially in the presence of atmospheric oxygen, iron ions in the spent fixer liquid precipitate as iron oxides which clog the drain and conduits through which the spent liquids flow together. This clogging results in flooding of surrounding areas with the liquids, requiring that the areas and the clogged drain and conduits be cleared.
The precipitation of the iron oxides from the iron ions of the spent fixer liquid arises as a result of the increase in pH when the spent fixer liquid contacts the highly alkaline spent developer liquid. This precipitation is enhanced in the presence of oxygen gas, such as is present in the atmosphere.
U.S. Pat. No. 5,792,347 of J. Riviere et al describes an effluent precipitation and neutralization vessel for spent fixer liquid and spent developer liquid, however, in that U.S. Patent the spent fixer liquid was acidic. Acidic fixer liquids are employed in black and white photographic processing and X-ray processing.
The problem of iron oxides precipitation and consequent clogging is more severe with the spent liquids employed in colour photography processing and may occur in all locations where the two spent liquids are in contact.